The semiconductor industry is now using copper interconnects in state of the art microprocessors. These embedded fine metal lines form the three-dimensional grid upon which millions of transistors at the heart of the microprocessor can communicate and perform complex calculations. Copper is chosen over the more conventionally used aluminum since it is a superior electrical conductor thereby providing higher speed interconnections of greater current carrying capability. These interconnect pathways are prepared by the damascene process whereby photolithographically patterned and etched trenches (and vias) in the dielectric insulator are coated with a conformal thin layer of a diffusion barrier material (for copper this is usually tantalum or tantalum nitride) and then completely filling in the features with pure copper. Excess copper is then removed by the process of chemical mechanical polishing. Since the smallest features to be filled can be less than 0.2 microns wide and over 1 micron deep, it is crucial that the copper metallization technique used is capable of evenly filling these deeply etched features without leaving any voids which could lead to electrical failures in the finished product. Copper chemical vapor deposition (CVD) is a technique that is well known for its ability to xe2x80x98gap fillxe2x80x99 such structures. In this process, a vapor of a volatile organometallic species containing copper is introduced to the surface to be metallized, whereupon a chemical reaction occurs in which only copper is deposited on the surface. Since the copper is delivered in a vapor form it evenly accesses both vertical and horizontal surfaces to yield a very evenly distributed film. Many precursors for copper CVD are known. The most desirable are those that are highly volatile, give pure copper films and do not introduce contaminating species into the reaction chamber or onto diffusion barrier surfaces. Currently, the biggest challenge facing copper CVD is its poor adhesion to tantalum-based diffusion barriers leading to delamination of the copper film during chemical mechanical polishing.
CVD copper precursors can be grouped into the following three major categories:
1. CVD copper using Cu(hfac)L type precursors where (hfac) represents 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate anion and (L) represents a neutral stabilizing ligand, usually an olefin an alkyne or a trialkylphosphine.
Many of these compounds are volatile liquids, the most well known being the compound Cu(hfac)tmvs, where tmvs is trimethylvinylsilane, known commercially as CupraSelect(copyright), available from Schumacher unit of Air Products and Chemicals, Inc., and described in U.S. Pat. No. 5,144,049. This class of precursors function by a process of disproportionation, whereby two molecules of Cu(hfac)L react together on a heated substrate surface to give copper metal, two molecules of free ligand (L) and the volatile by-product Cu(hfac)2. This is shown below in Equation (a):
2Cu(hfac)Lxe2x86x92Cu+Cu(hfac)2+2Lxe2x80x83xe2x80x83(a)
This process is typically run at around 200xc2x0 C. Note that in this process one half of the copper from the initial precursor cannot be utilized since it constitutes part of the Cu(hfac)2 by-product. One potential drawback of these precursors is their tendency to chemically degrade upon contact with tantalum or tantalum nitride diffusion barrier surfaces before the CVD copper film can begin to form. The chemical cause of this adverse reaction is thought to stem from the fluorocarbon character of the xe2x80x98hfacxe2x80x99 portion of the copper precursor rendering it reactive with tantalum. This degradation leads to a thin layer of chemical debris forming between the tantalum and copper. The lack of direct contact between the tantalum and copper is thought to cause three main effects. First, the mechanical adhesion between the two metals is compromised, resulting in their tendency for copper to delaminate under conditions of chemical mechanical polishing. Secondly, the chemical debris tends to act as an electrical insulator, resulting in poor electrical contact between the copper and the tantalum. Thirdly, since the copper is not growing directly onto the tantalum, it cannot replicate its crystal orientation, and hence, grows as a randomly oriented film (R. Kroger et al, Journal of the Electrochemical Society, Vol. 146, (9), pages 3248-3254 (1999)).
2. CVD Copper From Cu+2(X)2 
These compounds typically do not give pure copper films by CVD unless a chemical reducing agent, such as hydrogen, is used in the CVD processing, as shown below in Equation (b):
Cu(X)2+H2xe2x86x92Cu+2XHxe2x80x83xe2x80x83(b)
Examples of this type of precursor include; Cu+2 bis(xcex2-diketonates) (Wong, V., et al, Materials Research Society Symp Proc, Pittsburgh, Pa., 1990, pages 351-57; Awaya, N., Journal of Electronic Materials, Vol 21, No 10, pages 959-964, 1992), Cu+2 bis(xcex2-diimine) and Cu+2 bis(xcex2-ketoimine) compounds (U.S. Pat. No. 3,356,527, Fine, S. M., Mater. Res. Soc. Symp. Proc., 1990, pages 204, 415). These copper(+2) compounds are typically solids, and the CVD processing temperatures for them are typically above 200xc2x0 C. If these precursors are substantially fluorinated, then similar problems with adhesion, etc., are anticipated, as observed for the Cu(hfac)L compounds mentioned above.
3. CVD Copper From (Y)Cu(L) Compounds.
In these Cu(+1) precursors, (Y) is an organic anion and (L) is a neutral stabilizing ligand, such as trialkyphosphine. An example of such a precursor is CpCuPEt3, where Cp is cyclopentadienyl and PEt3 is triethylphoshine (Beech et al., Chem. Mater. (2), pages 216-219 (1990)). Under CVD conditions, two of these precursor molecules react on the wafer surface in a process whereby the two stabilizing trialkyphosphine ligands become disassociated from the copper centers, the two (Y) ligands become coupled together and the copper (+1) centers are reduced to copper metal. The overall reaction is shown below in Equation (c). However, this type of chemistry poses problems in a manufacturing environment, since the released trialkylphosphine ligands tend to contaminate the CVD chamber and can act as undesired N-type silicon dopants.
2(Y)Cu(L)xe2x86x922Cu+(Yxe2x80x94Y)+2(L)xe2x80x83xe2x80x83(c)
The present invention is directed to a group of novel homologous eight membered ring compounds having a metal, such as copper, reversibly, bound in the ring and containing carbon, nitrogen, silicon and/or other metals. A structural representation of the compounds of this invention is shown below [1]: 
wherein M and Mxe2x80x2 are each a metal, such as Cu, Ag, Au, and Ir; X and Xxe2x80x2 can be N or O; Y and Yxe2x80x2 can be Si, C; Sn, Ge, B, or Al; and Z and Zxe2x80x2 can be C, N, or O. Substituents represented by R1, R2, R3, R4, R5, R6, R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, R4xe2x80x2, R5xe2x80x2, and R6xe2x80x2 will vary depending on the ring atom to which they are attached. For example, R1, R2, R1xe2x80x2, and R2xe2x80x2 can each independently be an alkyl, an alkenyl, an alkynyl, a partially fluorinated alkyl, an aryl, an alkyl-substituted aryl, a partially fluorinated aryl, a fluoralkyl-substituted aryl, a trialkylsilyl, or a triarylsilyl; R3, R4, R3xe2x80x2, and R4xe2x80x2 can each be independently a hydrogen, an alkyl, a partially fluorinated alkyl, a trialkylsilyl, a triarylsilyl, a trialkylsiloxy, a triarylsiloxy, an aryl, an alkyl-substituted aryl, a partially fluorinated aryl, a fluoroalkyl-substituted aryl, or an alkoxy; and each of R5, R6, R5xe2x80x2, and R6xe2x80x2 can each independently be a hydrogen, an alkyl, an alkenyl, an alkynyl, a partially fluorinated alkyl, an aryl, an alkyl-substituted aryl, a partially fluorinated aryl, a fluoralkyl-substituted aryl, a trialkylsilyl, a triarylsilyl, a trialkylsiloxy, a triarylsiloxy, an alkoxy, a SiR7R8N(R9R10) group, or a SiR7R8OR11 group where R7, R8, R9, R10, and R11 can be an alkyl; provided that when X and Xxe2x80x2 are each O, there is no substitution at R2 and R2xe2x80x2; further provided that when Z and Zxe2x80x2 are each N, there is no substitution at R6 and R6xe2x80x2; and further provided that when Z and Zxe2x80x2 are each O, there is no substitution at R5, R6, R5xe2x80x2, or R6xe2x80x2. Alkyl and alkoxy each have 1 to 8 carbons; alkenyl and alkynyl each have 2 to 8 carbons; and aryl has 6 carbons.
A linear representation of one embodiment of the novel compounds of this invention is [xe2x80x94CuNMe2SiMe2CH2CuNMe2SiMe2CH2xe2x80x94] in which, according to structure [1] above, M and Mxe2x80x2 are each Cu; X and Xxe2x80x2 are each N; Y and Yxe2x80x2 are each Si; Z and Zxe2x80x2 are each C; R1, R2, R3, R4, R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, and R4xe2x80x2 are each methyl; and R5, R6, R5xe2x80x2, and R6xe2x80x2 are each H.
The compounds of this invention have the remarkable capability of depositing two metal atoms per molecule under chemical vapor deposition conditions by the process of thermal ligand coupling along with simultaneous reduction of the copper centers to copper metal. They are also well suited for use in Atomic Layer Deposition (ALD) of metal or oxide thin films, preferably copper or copper oxide films.
This invention is also directed to depositing metal and metal-containing films on a substrate, under ALD or CVD conditions, using the above novel compounds as precursors.